This invention relates generally to hydrocarbon conversion and, more specifically, to the catalytic halogenation of hydrocarbons.
As the uncertain nature of ready supplies and access to crude oil has become increasingly apparent, alternative sources of hydrocarbons and fuel have been sought out and explored. The conversion of low molecular weight alkanes (lower alkanes) to higher molecular weight hydrocarbons has received increasing consideration as such low molecular weight alkanes are generally available from readily secured and reliable sources. Natural gas, partially as a result of its comparative abundance, has received a large measure of the attention focused on sources of low molecular weight alkanes. Large deposits of natural gas, mainly composed of methane, are found in many locations throughout the world. In addition, low molecular weight alkanes are generally present in coal deposits and may be formed during numerous mining operations, in various petroleum processes, and in the above- or below-ground gasification or liquefaction of synthetic fuelstocks, such as coal, tar sands, oil shale and biomass, for example. In addition, in the search for petroleum, large amounts of natural gas are discovered in remote areas where there is no local market for its use as a fuel or otherwise. Additional major natural gas resources are prevalent in many remote portions of the world such as remote areas of western Canada, Australia, U.S.S.R. and Asia. Commonly, natural gas from these types of resources is referred to as "remote gas".
Generally, much of the readily accessible natural gas is used in local markets as the natural gas has a high value use as a fuel whether in residential, commercial or industrial applications. Accessibility, however, is a major obstacle to the effective and extensive use of remote gas. In fact, vast quantities of natural gas are often flared, particularly in remote areas from where its transport in gaseous form is practically impossible.
Conversion of natural gas to liquid products is a promising solution to the problem of transporting low molecular weight hydrocarbons from remote areas and constitutes a special challenge to the petrochemical and energy industries. The dominant technology now employed for utilizing remote natural gas involves its conversion to synthesis gas, also commonly referred to as "syngas", a mixture of hydrogen and carbon monoxide, with the syngas subsequently being converted to liquid products. While syngas processing provides a means for converting natural gas to a more easily transportable liquid that in turn can be converted to useful products, the intermediate step involved is such processing, i.e., the formation of the synthesis gas, is typically relatively costly as it involves adding oxygen to the rather inert methane molecule to form a mixture of hydrogen and carbon monoxide. While oxygen addition to the carbon and hydrogen of methane molecules may be advantageous when the desired products are themselves oxygen containing, such as methanol or acetic acid, for example, such oxygen addition is generally undesirable when hydrocarbons such as gasoline or diesel fuel are the desired products as the added oxygen must subsequently be removed. Such addition and removal of oxygen naturally tends to increase the cost involved in such processing.
Methane, the predominant component of natural gas, although difficult to activate, can be reacted with oxygen or oxygen-containing compounds such as water or carbon dioxide to produce synthesis gas. Synthesis gas can be converted to syncrude such as with Fischer-Tropsch technology and then upgraded to transportation fuels using usual refining methods. Alternatively, synthesis gas can be converted to liquid oxygenates which in turn can be converted to more conventional transportation fuels via catalysts such as certain zeolites.
Because synthesis gas processing requires high capital investment, with the syngas being produced in relatively energy intensive ways, such as by steam reforming where fuel is burned to supply heat for reforming, and represents an indirect route to the production of hydrocarbons, the search for alternate means of converting methane directly to higher hydrocarbons continues.
One such alternative method involves methane conversion to higher hydrocarbons via a "chlorine-assisted" route, such as represented by the following 2-step process: EQU CH.sub.4 +HCl+O.sub.2 .fwdarw.chloromethanes+H.sub.2 O (1) EQU chloromethanes.fwdarw.C.sub.2+ hydrocarbons+HCl (2)
In the first step of such a process, methane (using HCl and oxygen) is chlorinated to chloromethanes. Such a chlorination step is also referred to as methane "oxychlorination" or "oxyhydrochlorination".
In the second step of such a process, chloromethanes are converted to higher hydrocarbons, e.g., hydrocarbons having 2 or more carbon atoms, represented by "C.sub.2+ ", and HCl. The HCl generated in the second step can be recycled back to the first step so that effectively there is no net consumption of chlorine in the overall process.
Such a chlorine-assisted process is not yet practiced commercially.
Catalysts for the chlorination of the hydrocarbons, such as methane, have in the past typically consisted of copper chloride and promoters such as potassium and lanthanum chlorides supported on silica or alumina. For example, see Applied Catalysis, Vol. 11, pp. 35-71 (1984); J. Catalysis, Vol. 99, pp. 12-18 (1986); European Patent Application 0117731, filed Sept. 5, 1984, by British Petroleum; and U.S. Pat. No. 4,123,389 issued Oct. 31, 1978, and assigned to Allied Chemical Corporation.
The role of the potassium and/or lanthanum chloride promoter in such catalysts is not fully understood. It is believed that the presence of such a promoter results in the formation of a supported eutectic mixture of the copper chloride and promoter chloride, which mixture is molten at reaction temperatures. Catalytic activity is believed to be facilitated by the enhanced mass transfer properties of a molten phase relative to a similar composition in a solid phase.
Generally, while such catalysts initially appear relatively active and selective, the use of such catalysts suffers from relatively rapid catalyst deactivation realized during such use of the catalyst. Such deactivation is believed to be due to changes in the active copper species of the catalyst with time as the catalyst is on stream.
In addition, U.S. Pat. Nos. 4,052,468; 4,052,470; 4,060,555; and 4,105,691, all assigned to Allied Chemical Corporation, relate to processes for the production of chlorofluorinated hydrocarbons, such as cycloaliphatic, acyclic, aliphatic ketones and carboxylic acids, respectively, via the use of a Deacon catalyst (such as a metal halide impregnated on a suitable carrier).
Noceti, et al., U.S. Pat. No. 4,769,504, discloses a process for the production of aromatic-rich, gasoline boiling range hydrocarbons from lower alkanes, particularly from methane. The process is carried out in two stages. In the first stage, an alkane is reacted with oxygen and hydrogen chloride over an oxyhydrochlorination catalyst such as copper chloride with minor proportions of potassium chloride and rare earth chloride. This produces an intermediate gaseous mixture containing water and chlorinated alkanes. In the second stage, the chlorinated alkanes are subsequently contacted with a crystalline aluminosilicate catalyst in the hydrogen or metal promoted form to produce gasoline range hydrocarbons with a high proportion of aromatics and a small percentage of light hydrocarbons (C.sub.2 -C.sub.4). The light hydrocarbons can be recycled for further processing over the oxyhydrochlorination catalyst.
The search for a long-lived catalyst effective in catalyzing the halogenation, particularly the chlorination, of hydrocarbons, particularly lower hydrocarbons, especially methane, has continued.
Catalytically active copper aluminum borate is the subject of commonly assigned Satek U.S. Pat. No. 4,590,324; of commonly assigned Kouba, et al., U.S. Pat. No. 4,613,707; of commonly assigned Zletz, et al., U.S. Pat. No. 4,645,753; of commonly assigned Zletz, U.S. Pat. No. 4,729,979; of commonly assigned De Simone, et al., U.S. Pat. No. 4,755,497; and of commonly assigned copending application Zletz, U.S. Ser. No. 285,103 filed Dec. 14, 1988. These patents and application disclose the preparation, characterization and utility of copper aluminum borate and are hereby incorporated by reference. None of these patents, however, disclose or suggest the use of crystalline copper aluminum borate in a process for the halogenation and, in particular, the chlorination of hydrocarbons.
Further, McArthur, in U.S. Pat. Nos. 3,856,702, 3,856,705 and 4,024,171, discloses that it has been long the practice in the art to impregnate or otherwise distribute active catalytic metals support materials having desired properties of porosity, surface area, thermal and mechanical stability, and suitably inert chemical properties. McArthur teaches that a superior catalyst support results from calcining certain alumina and boria composites within the temperature range of about 1,250.degree. F.-2,600.degree. F., which appears to produce a defined crystalline phase of 9 Al.sub.2 O.sub.3.2B.sub.2 O.sub.3, following which the aluminum borate support can be impregnated with solution(s) of desired catalytic salt or salts, preferably those that are thermally decomposable to give the corresponding metal oxides. Following impregnation, the finished catalysts are dried and, if desired, calcined at temperatures of 500.degree. to 1000.degree. F., for example. In the final catalyst, the active metal or metals may appear in the free form as oxides or sulfides or in another active form. Examples 1 to 6 of McArthur impregnate the calcined support with an aqueous solution of copper nitrate and cobalt nitrate to provide about 4% copper as CuO and 12% cobalt as Co.sub.2 O.sub.3 in the final catalyst.
Uhlig, in Diplomarbeit, Institute for Crystallography, Aacken (October 1976) "Phasen - und Mischkristall - Bildung im B.sub.2 O.sub.3 - armeren Teil des Systems Al.sub.2 O.sub.3 -CuO-B.sub.2 O.sub.3 " ("Formation of Phases and Mixed Crystals in that Part of the Al.sub.2 O.sub.3 -CuO-B.sub.2 O.sub.3 System With a Low B.sub.2 O.sub.3 Content") which is hereby incorporated by reference, discloses preparation of a green tetragonal solid copper aluminum borate having the structure Cu.sub.2 Al.sub.6 B.sub.4 O.sub.17 by grinding together solid boron oxide, copper oxide and alumina, sealing the ground metal oxides in a platinum tube and heating same at 1000.degree. C. for a period of 48 hours. Attempts to produce this copper aluminum borate by the indicated route yield well-defined, dense crystalline particles which have an extremely low surface area and are accordingly not suitable for many catalysis processes due to the low porosity and surface area.
Also, Asano, U.S. Pat. No. 3,971,735, discloses a copper-, zinc-, aluminum- and boron-containing catalyst useful in low temperature methanol synthesis. The catalyst is preferably produced by forming a mixture of water-soluble salts of copper, zinc and boron, precipitating same with an alkali carbonate and mixing with alumina. The catalyst is then fired at approximately 300.degree.-450.degree. C.